In general, the ink jet printing is carried out by discharging liquid ink on a print paper. In other words, the ink jet printer head is provided with arrayed nozzles each having a size of needle tip, from which the liquid ink is sprayed towards the print paper. Although the basic principle is same, the ink jet printing is categorized into a bubble jet type, a thermal jet type and a piezoelectric type according to the ink discharging mode.
In the bubble jet spraying type, a heater disposed on the side wall of a micro tube controls the size of bubbles in order to spray ink. That is, the heater is operated to generate bubbles, and then the ink is sprayed when the bubble is expanded to its maximum size. After spraying, if the heating is stopped, ink is newly supplied as the bubble is diminished. This type of ink jet printing is advantageous in that it does not need an ink storage and a small sized head can be realized since the tube and heater are very small. However, it is very difficult to array the nozzles in a two-dimensional pattern.
The thermal jet type is similar to the above-mentioned bubble jet, but the position of a heater is different therefrom. In this type, the heater is disposed on the same or opposite side of the nozzle, and when the heated ink is vaporized, the ink is sprayed due to the vapor pressure thereof. Therefore, one of the biggest advantages of this type resides in that the heater and nozzle can be arrayed in a two-dimensional pattern, and therefore, it is relatively easy to increase the number of nozzles.
In the piezoelectric spraying type, ink is discharged by an impact from behind a nozzle according to an input signal as in the conventional syringe operation. As the driving force for discharging ink, a piezoelectric element is employed, which changes its shape in response to voltage variation. Specifically, when a voltage is applied, the piezoelectric element is deformed and the liquid surface at the tip of the nozzle is swollen. Instantly, if the liquid surface is pulled back by controlling the voltage, then ink ahead of the nozzle face is sprayed forward due to its momentum.
Among the above-described types, the bubble jet and thermal jet types necessitate a relatively small space for the heater for generating the ink spraying force, as compared with the actuator in the piezoelectric spraying type. Furthermore, in the bubble and thermal jet types, an ink chamber and an ink storage may be disposed on the same plane so that the density of nozzles can be fairly increased. In contrast, the piezoelectric type has a disadvantage in that the number of nozzles or the nozzle density cannot be readily increased due to the complicated structure thereof.
FIG. 1 shows a schematic configuration of the conventional piezoelectric ink jet print head, which is exemplified by U.S. Pat. No. 5,748,214.
As depicted in FIG. 1, the conventional ink jet printer head is composed of a port for supplying ink (not shown), an ink storage 42 for storing the ink supplied through the port (not shown), a chamber 15 for receiving ink from the ink storage 42, a nozzle 21 for discharging ink from the chamber 15, and an actuator for exerting pressure to the chamber, i.e., the ink therein in order to discharge the ink through the nozzle 21 via a nozzle connection 20.
The above-mentioned actuator includes a resilient plate 13, a lower electrode 16 disposed on the resilient plate 13, a piezoelectric plate 17 disposed on the lower electrode 16, and an upper electrode 18 placed on the piezoelectric plate 17.
The chamber 15 is defined by the resilient plate 13 disposed thereabove, a spacer 12 placed in the side thereof, and a sealing plate 11 placed therebelow.
In addition, the ink storage 42 is constituted by an ink supplying plate 24 where upper through-holes 26 and 40 are formed, an ink storage forming plate 23 on the side thereof, and a nozzle plate 30 disposed therebelow. The nozzle for spraying ink is formed in the nozzle plate 30.
In operation, when an electric power is applied to the actuator, the piezoelectric plate 17 is deformed and exerts a pressure to the chamber 15, and thus, the ink inside the chamber 15 is discharged through the nozzle 21 due the pressure applied thereto.
On the other hand, U.S. Pat. No. 6,217,158B1 discloses an ink jet printer head similar to the above-described patent, except that it does not have the resilient plate disposed below the lower electrode.
The above-mentioned conventional ink jet printer heads embrace several problems and disadvantages. The conventional head necessitates a separate ink storage and, therefore, cannot use the space and area efficiently so an efficient arrangement of elements or components can be readily achieved. Also, this results in significant reduction in the number of nozzles, i.e., the nozzle density.
In addition, the nozzle portion is formed by laminating plural plates, and the ink storage must be included, together with the nozzle portion, in the structure formed by the lamination of plates. This causes a complexity in the fabricating process, and deteriorates its space efficiency.
Another drawback is caused by the fact that the cross section leading to the nozzle portion from the chamber is steeply changed. Therefore, it imposes an inevitable limitation in generating fine ink drops.
Furthermore, the ink-supplying path from the port to the chamber is disadvantageously bent, so that the ink bubbles (F) are apt to be trapped in the ink-supplying path.